Various portable electronic measuring instruments are currently available. One example of such an instrument is a displacement measuring instrument, a hand-held electronic caliper which can be used for making precise measurements of machined parts to ensure that they are meeting tolerance requirements. It is obvious that the less power such instruments use, the fewer batteries (or other power sources) they will require and the longer they will operate before the batteries (or other power sources) need to be replaced or replenished. However, reducing the power requirements of such devices is a complex task. Such devices are required to make highly accurate measurements, and the complex signal processing techniques that have been developed for such devices tend to complicate the process of designing circuitry that will both accomplish the desired accuracy and operate at low voltage and power levels.
An example of an electronic caliper using highly accurate measuring techniques is shown in U.S. Pat. No. 5,901,458, which is commonly assigned and hereby incorporated by reference in its entirety. As described, the electronic caliper has a reduced offset position transducer that uses a read head that is movable along a scale. The electronics provide a precise measurement of the read head's position on the scale. The transducer uses two sets of coupling loops on the scale to inductively couple a transmitter winding on the read head on a slide to one or more receiver windings on the read head. The transmitter winding generates a primary magnetic field. The transmitter winding is inductively coupled to first loop portions of first and second sets of coupling loops by a magnetic field. Second loop portions of the first and second sets of coupling loops are interleaved and generate secondary magnetic fields. A receiver winding is formed in a periodic pattern of alternating polarity loops and is inductively coupled to the second loop portions of the first and second sets of coupling loops by the secondary magnetic fields. Depending on the relative position between the read head and the scale, each polarity loop of the receiver winding is inductively coupled to a second loop portion of either the first or second set of coupling loops. The relative positions of the first and second loop portions of the first and second sets of coupling loops are periodic and dependent on the relative position of the coupling loops on the scale.
Another example is shown in U.S. Pat. No. 5,886,519, which is commonly assigned, and incorporated herein by reference in its entirety. The '519 patent discloses an inductive absolute position transducer for high accuracy applications, such as linear or rotary encoders, electronic calipers and the like. The absolute position transducer uses two members movable relative to each other. The first member contains at least one active transmitter for generating a magnetic field and at least one receiver for receiving the generated magnetic field. The passive second member includes passive flux modulating elements that modulate the received field depending on their position relative to the at least one receiver. An electronic circuit coupled to the at least one transmitter and the at least one receiver compares the outputs of the at least one receiver, evaluates the absolute position between the two members, and exhibits the position on a display. The inductive absolute position transducer determines the absolute position between the two members.
Systems such as those shown in the '458 and '519 patents utilize advanced signal processing techniques to produce highly accurate displacement measurements. The present invention is directed to a portable electronic measuring instruments, and especially to portable electronic displacement measuring instruments, that produces highly accurate measurements while using a low voltage low power system.